Radio frames in a Long Term Evolution (LTE) system and an LTE-Advanced (LTE-A) system include frame structures of a Frequency Division Duplex (FDD) mode and a Time Division Duplex (TDD) mode. FIG. 1 is a schematic diagram of a frame structure in an existing LTE/LTE-A FDD system. As shown in FIG. 1, a radio frame of 10 milliseconds (ms) consists of 20 slots having a length of 0.5 ms and numbered from 0 to 19, and a subframe i having a length of 1 ms is formed by the slot 2i and the slot 2i+1.
FIG. 2 is a schematic diagram of a frame structure in an existing LTE/LTE-A TDD system. A radio frame of 10 ms consists of two half frames having a length of 5 ms, either of which includes 5 subframes having a length of 1 ms. A subframe i is defined as two slots which are 2i and 2i+1 respectively having a length of 0.5 ms, and an uplink-downlink configuration supported by the subframe is as shown in Table 1:
TABLE 1Uplink-downlinkUplink-downlinkTransition pointSubframe numberconfigurationcycle01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD6 5 msDSUUUDSUUD
where for each subframe in a radio frame, “D” represents a dedicated subframe for downlink transmission, “U” represents a dedicated subframe for uplink transmission, “S” represents a special subframe, including three parts, a Downlink Pilot Time Slot (DwPTS), a Guard Period (GP) and an Uplink Pilot Time Slot (UpPTS).
In the two frame structures above, a time slot in a normal Cyclic Prefix (CP) includes 7 symbols having a length of 66.7 microseconds (us), in which the CP length of a first symbol is 5.21 us, and the CP length of the remaining 6 symbols is 4.69 us; and a time slot in an Extended CP includes 6 symbols, and the CP length of all symbols is 16.67 us.
In the LTE/LTE-A system, a Hybrid Automatic Repeat Request (HARQ) process includes that when a base station or a terminal needs to transmit data, the base station sends the data through downlink signaling and distributes information required by the transmission, such as resource allocation information. The sender sends the data according to the information while saving the data in a cache of the sender itself for retransmission. After receiving the data, a receiver detects the data, and sends Acknowledged (ACK) information to the sender if the data is received correctly. After receiving the ACK information, the sender clears the cache used in the transmission and terminates the transmission. If the data is not received correctly, Non-Acknowledged (NACK) is sent to the sender, and a packet not received correctly is saved in a cache of the receiver. After receiving the NACK, the sender extracts the data from its cache, and retransmits the data with a specific packet format on a corresponding subframe and a corresponding frequency-domain position. After receiving the retransmitted packet, the receiver combines the retransmitted packet with the packet that is not correctly received previously and performs detection again. Subsequently, the process above is repeated until the data is received correctly or the number of transmission times exceeds a maximum number threshold of transmission times.
In the LTE/LTE-A system, timing of scheduling for a Physical Downlink Share Channel (PDSCH) in a downlink HARQ follows the following rule, that is, scheduling for the downlink HARQ follows the following rule: a User Equipment (UE) detects a Physical Downlink Control Channel (PDCCH) on a subframe n and receives and detects a PDSCH on a current subframe according to information of the PDCCH.
In an LTE/LTE-A FDD system, transmission of HARQ-ACK of a PDSCH in a downlink HARQ, that is, a timing relation of the downlink HARQ follows the following rule: a UE detects transmission of a PDSCH on a subframe n, or instructs a PDCCH of downlink Semi-Persistent Scheduling (SPS) release, and transmits a corresponding HARQ-ACK response on a subframe n+4. In an LTE/LTE-A TDD system, a timing relation of a downlink HARQ follows the following rule: a UE detects transmission of a PDSCH on a subframe n−k or instructs a PDCCH on downlink SPS release, and transmits a corresponding HARQ-ACK response on an uplink subframe n, wherein k belongs to K, and the values of K in different uplink-downlink configurations are as shown in Table 2.
TABLE 2Uplink-downlinkSubframe number nconfiguration01234567890——6—4——6—41——7, 64———7, 64—2——8, 7, 4, 6————8, 7, 4, 6——3——7, 6, 116, 55, 4—————4——12, 8, 7, 116, 5, 4, 7——————5——13, 12, 9, 8, 7,———————5, 4, 11, 66——775——77—
In the LTE/LTE-A FDD system, an HARQ timing of a Physical Uplink Share Channel (PUSCH) is stipulated as follows: given that the UE detects HARQ information on a downlink subframe n, then the information corresponds to a PUSCH that needs to be sent by the UE on an uplink subframe n−4.
In the LTE/LTE-A TDD system, an HARQ timing of a PUSCH is stipulated as follows.
Given that the UE detects HARQ information on a downlink subframe n, the information may be sent through a PDCCH or a Physical HARQ Indicator Channel (PHICH). In uplink-downlink configurations 1 to 6 and configuration 0 (I_PHICH parameter=0), the information corresponds to a PUSCH sent by the UE on an uplink subframe n−k. The values of k in different uplink-downlink configurations for different uplink-downlink configuration and subframe indexes are as shown in Table 3.
TABLE 3Uplink-downlink Subframe number nconfiguration01234567890747414646266366646656664746
In uplink-downlink configuration (I_PHICH parameter=1), given that the UE detects HARQ information on a downlink subframe n, then the information corresponds to a PUSCH sent by the UE on a uplink subframe n−6. Since uplink and downlink subframes are in one-to-one correspondence in the LTE/LTE-A FDD system, the UE needs to feed back ACK/NACK response information of 1 bit when a PDSCH only includes one transmission block, and the UE needs to feed back ACK/NACK response information of 2 bits when the PDSCH includes 2 transmission blocks. The UE uses Physical Uplink Control Channel (PUCCH) format 1a/1b to send ACK/NACK response information of half a bit. Since uplink and downlink subframes are not in one-to-one correspondence in the LTE/LTE-A TDD system, ACK/NACK response information corresponding to a plurality of downlink subframes needs to be sent on a PUCCH of an uplink subframe, wherein a set of downlink subframes corresponding to the uplink subframe form a “bundling window”. The ACK/NACK response information is sent by two ways. The first one is bundling, and the core idea of this way is to perform logics and an operation on the uplink frame-fed back ACK/NACK response information of transmission blocks corresponding to the downlink subframes. If a downlink subframe has 2 transmission blocks, the UE needs to feed back ACK/NACK response information of 2 bits, and if each subframe only has 1 transmission block, the UE needs to feed back ACK/NACK response information of 1 bit. The UE applies PUCCH format 1a/1 b to send the ACK/NACK response information of 1 or 2 bits. The other way is multiplexing (multiplexing with channel selection). The core idea of this way is to use different PUCCH channels and modulation symbols on the channels to represent different uplink subframe-fed back feedback states of the downlink subframes. If there are a plurality of transmission blocks on a downlink subframe, logics and spatial bundling are performed on ACK/NACK fed back by the plurality of transmission blocks of the downlink subframe first and channel selection is performed subsequently. The UE applies format 1b with channel selection to send the ACK/NACK response information.
Compared with an LTE system, the most significant characteristic of an LTE-A system is that the LTE-A system introduces a carrier aggregation technology. In other words, bandwidths of the LTE system are aggregated to acquire a larger bandwidth. In the system in which carrier aggregation is introduced, an aggregated carrier is called a Component Carrier (CC), also known as a cell. In the meanwhile, the concept of a Primary Component Carrier/Cell (PCC/PCell) and a Secondary Component Carrier/Cell (SCC/SCell) is also proposed. The system with carrier aggregation at least includes a primary cell and a secondary cell, wherein the primary cell is always in an activated state and it is stipulated that downlink HARQ information is transmitted only on a Pcell.
In an LTE-A carrier aggregation system, 2 sending methods are defined to send an HARQ-ACK response message on a PUCCH: PUCCH format 1b with channel selection and PUCCH format 3. If a UE configured with a plurality of serving cells can only aggregate 2 serving cells maximally, the UE will send HARQ-ACK by means of PUCCH format 1b with channel selection when configuring the plurality of serving cells, and if the UE is able to support aggregation of more than 2 serving cells, a base station will further uses signaling of a higher layer to configure whether the UE sends HARQ-ACK response information by means of PUCCH format 1b with channel selection or PUCCH format 3 when the UE configures the plurality of serving cells.
An existing carrier aggregation technology is only applied to an FDD cell or a TDD cell. However, an operator generally has an FDD spectrum and a TDD spectrum at the same time during practical application. Therefore, it is of great importance to support aggregation of an FDD cell and a TDD cell so as to improve spectral efficiency and user experience. In this process, selection of a type of an HARQ timing to send a PDSCH/PUSCH of each cell after aggregation of the FDD cell and the TDD cell is of crucial significance for effective aggregation of the FDD cell and the TDD cell. A common solution in the traditional art may be called a “double mode” solution. That is, a PDSCH/PUSCH of a TDD cell is processed according to an HARQ timing of existing LTE/LTE-A TDD while a PDSCH/PUSCH of an FDD cell is processed according to an HARQ timing of existing LTE/LTE-A FDD. However, this solution has big defects, specifically described as follows:
1, when a network performs downlink aggregation on a plurality of cells (including at least one FDD cell and at least one FDD cell) for a UE, the solution requires that the UE has the ability to feed back an HARQ on two cells at the same time, which reduces the power amplification efficiency and uplink coverage of the UE and increases the cost for implementing the UE; and
2, advantages of cross carrier scheduling cannot be fully supported and utilized. For example, a PDSCH/PUSCH cannot be supported on an FDD cell, and a corresponding PDCCH cannot be supported on a TDD cell, which is unfavorable for full utilization of resources of the two types of cells after aggregation of the FDD cell and the TDD cell, thus further limiting improvement of the aggregation performance of the FDD cell and the TDD cell.
Therefore, a method is provided here to effectively aggregate an FDD cell and a TDD cell, thus effectively solving the problem above, fully and effectively utilizing FDD and TDD resources, and facilitating implementation of existing base station and terminal.